[A6] A6 sine osc

Sun Mar 13 17:42:22 PST 2005

I did some tests using a lab grade oscilloscope, and turning everything off except the oscillators to try to get as pure a signal output as I could. Here's what I found. The oscillators are pretty clean but they don't have perfect shape waveforms. The sine wave has a slight taper towards the top and bottom (peaks), with a small but noticeable point to them. This is with the pre filter mix set at 50% and sub osc at 0. The triangle pattern exhibited a slight waviness to it's leading and trailing edges.   When I turned the mix up to 100% there was noticeable clipping but only at the top (+side) of the waveform. Strange to say the least. Then I turned up only the sub osc and there was an odd reshaping with clipping again only at the top. The same thing occurs with other waveforms. They all seam to have an imperfect form but not enough to be alarming, just strange. The problems are exacerbated by adding post filter mixing. Conclusion, The biggest problem with A6 is that the mixing is too powerful for the buffers which causes distortion at even medium levels, let alone high levels. The biggest curiosity is that when I compared the waveforms to those of my Oberhiem OB-8, the 8 fared far better. It's waveforms were near perfect as compared to the A6. It sounds cleaner too. This is surprising, since this is from a 21 year old synth!! No wonder I prefer the sound of my Obie. This experience confirms what others have said. Keeping the mixes turned down results in a smoother, more classic sound as opposed to the raspy, edgy sound you get with most of the presets. I will try to post a link to pics I took of the waveforms when I get a chance. BTW, the waveform that was originally posted by Kim looks like it either has a harmonic attached or some effect, but it is not a single clean form.

________________________________

From: a6-bounces at code404.com on behalf of Shawn O.
Sent: Sun 3/13/2005 6:23 PM
To: Wayne Rudd; A6 mailing list
Subject: Re: [A6] A6 sine osc

I keep temp and background tuning off,. every day when I power them on I
do a full tune ,.. all ocs, filters, VCA, doesnt make a difference.

Wayne Rudd wrote:

>Have you tried a VCA tune.?..came up on the list a little while ago that the
>Auto Tune doesn't include the VCA's...you need to choose that specifically
>from the tune menu.
>
>cheers, Wayne.
>
>
> 
>
>>------------------------------
>>
>>Message: 3
>>Date: Sat, 12 Mar 2005 21:06:49 -0800
>>From: "Shawn O." <sobrien at wavecable.com>
>>Subject: Re: [A6] A6 sine osc
>>To: Kim Johnsson <kim.johnsson at ineo.fi>,      A6 mailing list
>>      <a6 at code404.com>
>>Message-ID: <4233CA69.7070008 at wavecable.com>
>>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> >So, is this the standard A6 version of a sine wave, or is it just mine
>>
>>that's a bit bent?
>>
>>
>>I have 2 Andromeda's now and checked this out on both of them, same
>>thing, this is at really low frequencies that this occurs,. happens with
>>
>>triangle and square waves as well, correct me if I am wrong I believe
>>this is actually how the moog modular VCO of the time performed with its
>>
>>older component discrete construction,
>>
>>I would guess modules from Modcan and MOTM have much better tracking
>>with producing sine waves that are pure at low frequency levels, both of
>>
>>those companies seem to be into producing analogue perfection.
>>
>>One thing that makes me scratch my head is how the same FM patch on two
>>
>>different Andromeda's does not sound the same at all, well even between
>>
>>different voice chips when you are cycling through on patches that use
>>allot of FM,
>>
>>also of note, so far 2 out of 3 Andromeda's that I have had my hands on
>>
>>display an interesting amplification of white noise on at least 1 of the
>>
>>voices playing the patch Amsterdam kick patch in rotary mode (think this
>>
>>is preset1 81), on some voices the amplification of white noise is
>>subtle, on others it is very noticeable, my work around for this is
>>saving that patch to the user bank and turning the white noise off or
>>assigning it to play on a voice that the noise is not noticeable.
>>
>>I think this is a problem with the way the ASIC's are manufactured where
>>
>>something gets screwy in the VCA portion of the chip during lithography,
>>
>>kind of makes me wounder how much better of an instrument this would be
>>
>>if the voice chips were larger or had 1 voice on each instead of 2.
>>
>>~Shawn O'Brien
>>
>>   
>>
>
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